Water repellent coating film, method and apparatus for manufacturing the same, and water repellent coating material composition

ABSTRACT

By forming a film that comprises a microcrystalline polymer having at least a fluorocarbon group and has a rough surface on a surface of a base material, super-water-repellency is provided, the dew condensation water of an air conditioner, for example, can be easily removed, and the freezing of the fin of the heat exchanger can be prevented. A fin that is made of aluminium is coated with a solution for forming a coating film, in which CF 3  (CF 2 ) 7  --(CH 2 ) 2  --SiCl 3  is diluted with nonaqueous cyclohexamethyl trisiloxane at a concentration of 10 vol. % for preparation, to a thickness of 1 to 10 μm by a brush, and then the cyclohexamethyl trisiloxane is vaporized in an atmosphere having a relative humidity of about 75% at room temperature. CF 3  (CF 2 ) 7  --(CH 2 ) 2  --SiCl 3  that remained on the fin is rapidly hydrolyzed with the moisture in the atmosphere, and the moisture in air and a --SiCl 3  group dehydrochlorinated to form a microcrystalline polymer on the fin. As a result, a coating film having a surface roughness in the range of 1 to 40 μm and a contact angle of about 171° to water can be formed.

FIELD OF THE INVENTION

The present invention relates to a water repellent coating film, amethod and an apparatus for manufacturing the same, and a waterrepellent coating material composition, and more particularly to a waterrepellent coating film that comprises a microcrystalline polymer havingat least a fluorocarbon group and has a rough surface.

BACKGROUND OF THE INVENTION

Conventionally, a method for coating a surface with a hydrophilic resinis used for the fin of the heat exchanger of an air conditioner, etc. inorder to more readily eliminate dew condensation water during operation.However, with traditional methods for making a surface hydrophilic, dewcondenses and freezes, i.e., frost forms, particularly during winter incold environments. This frozen water is difficult to eliminate andreduces operating efficiency. In fact, air conditioning operation mustbe occasionally stopped to melt and remove the frost which builds up.

Thus, both an extra heater, and enregy it uses, is required for removingfrost. Also, such a process is not desired as air conditioning operationmust be occasionally stopped.

SUMMARY OF THE INVENTION

In order to solve conventional problems, the present invention seeks toprovide a coating film that has a high contact angle to a water drop andexcellent water repellency as well as a method for manufacturing thesame. Further, the present invention aims to provide a water repellentcoating film that facilitates removal of the dew which condenses on anair conditioner to prevent the fin of the heat exchanger from freezingand allow continuous operation of air conditioning.

In one aspect, a first coating film of the present invention comprises apolymer having a fluorocarbon group formed on a surface of a substrate,wherein the film comprises a microcrystalline polymer and has a roughsurface, and a part of molecules forming the film are covalently bondedto the surface of the substrate. Such a structure can provide a coatingfilm that has a high contact angle to a water drop and excellent waterrepellency. Also, the structure can improve the water separation of thesurface of the base material.

In the above structure, it is preferable that the microcrystallinepolymer having a fluorocarbon group is crosslinked by at least asiloxane (--SiO--) bond or a titanium-oxygen (--TiO--) bond. Thisexample can provide excellent durability and improve the waterseparation of the surface of the base material.

A second coating film of the present invention comprises a fine particleor a whisker as a core and a microcrystalline polymer having afluorocarbon group that is formed to "wrap" the fine particle or thewhisker, and has a rough surface. Such a structure can provide a coatingfilm that has a high contact angle to a water drop and has excellentwater repellency. Also, the structure can improve the water separationof the surface of the base material.

In the above structure, it is preferable that the microcrystallinepolymer having a fluorocarbon group is crosslinked by at least asiloxane (--SiO--) bond or a titanium-oxygen (--TiO--) bond. Thisexample can provide excellent durability and improve the waterseparation of the surface of the base material.

In the above structure, it is further preferable that themicrocrystalline polymer having a fluorocarbon group that is crosslinkedby a siloxane bond or a titanium-oxygen bond is formed by a hydrolysisreaction. This can provide a less impurity content and excellentdurability and improve the water separation of the surface of the basematerial.

In the above structure, it is still further preferable that theroughness of the surface is in the range of 0.1 to 100 μm. This canprovide a less impurity content, excellent durability, andsuper-water-repellency, and improve the water separation of the surfaceof the base material.

In the above structure, it is preferable that the roughness of the filmis in the range of 0.1 to 100 μm. This can provide excellent durabilityand super-water-repellency and improve the water separation of thesurface of the base material.

In the above structure, it is preferable that the film is cloudy with acolor of white or is opaque. This can provide high crystal strength,excellent durability, and super-water-repellency, and improve the waterseparation of the surface of the base material.

A water repellent heat exchanger fin according to the present inventioncomprises a water repellent coating film that has a fluorocarbon groupand a rough surface and is formed on a surface of a base material. Thisstructure can effectively remove the dew that condenses on an airconditioner to prevent the fin of the heat exchanger from freezing andallow continuous operation of air conditioning.

In the above structure, it is preferable that the water repellentcoating film is formed on a surface of a base material which, duringprocessing, is provided with a rough surface. In other words, by formingthe film that comprises a microcrystalline polymer having a fluorocarbongroup and has a rough surface on the surface of the base material, thewater separation of the surface of the base material of the waterrepellent heat exchanger fin can be improved.

In the above fin, it is preferable that the roughness of the surface ofthe base material is in the range of 0.1 to 50 μm. This structure isunlikely to cause the peeling of the coating film. The structure canprovide excellent durability and super-water-repellency and improve thewater separation of the surface of the base material.

An air conditioner according to the present invention uses a fin with awater repellent coating film formed in the heat exchange part. Thisstructure can provide an energy-saving air conditioner that has veryhigh water repellent efficiency and provides excellent amenity. In otherwords, this structure can easily remove the dew that condenses on an airconditioner even in cold environments to prevent the fin of the heatexchanger from freezing and allow continuous operation of airconditioning.

A water repellent coating material composition of the present inventioncomprises at least a material that has a hydrolyzable group having Si orTi and a fluorocarbon group, a fine particle or a whisker, and anonaqueous organic solvent. This coating material can provide a waterrepellent coating film with a very high manufacturing efficiency.

In the above water repellent coating material composition, it ispreferable that the nonaqueous organic solvent is at least one solventselected from the group consisting of xylene, toluene, normal paraffin,and silicone. The use of such a solvent allows efficiently growing amicrocrystal in manufacturing a water repellent coating film.

In the above water repellent coating material composition, it ispreferable that, as the material that has a hydrolyzable group having Sior Ti and a fluorocarbon group, a material that is expressed by CF₃--(CF₂)_(n) --(R)_(m) --SiX_(p) Cl_(3-p) is used as a main component, inwhich n represents 0 or an integer, R represents an alkylene group, avinylene group, an ethynylene group, an arylene group such as phenylenegroup, silicon, or a substituent having an oxygen atom, m represents 0or 1, X represents H, an alkyl group, an alkoxy group, an isocyanategroup, a fluorine-containing alkyl group, or a fluorine-containingalkoxy group, and p represents 0, 1, 2 or 3. By using such a material,the water repellency and durability of the coating film can be furtherimproved.

In the above composition, it is preferable that the amount of thematerial that has a hydrolyzable group having at least one elementselected from the group consisting of Si and Ti and a fluorocarbon groupis 1 to 50% by weight, the amount of at least one filler selected fromthe group consisting of a fine particle and a whisker is 1 to 30% byweight, and the amount of the nonaqueous organic solvent is 20 to 98% byweight based on the total weight of the composition.

A method for manufacturing a first water repellent coating film of thepresent invention comprises coating a surface of a base material with amaterial that has a hydrolyzable group having at least Si or Ti and afluorocarbon group in one molecule, and hydrolyzing a coating filmcomprising the material in an atmosphere containing moisture to providea film comprising a microcrystalline polymer having a fluorocarbon groupthat is at least crosslinked by a siloxane bond or a titanium-oxygen(--TiO--) bond. This structure can efficiently provide a coating filmthat has excellent durability, super-water-repellency, and excellentwater separation.

A method for manufacturing a second water repellent coating film of thepresent invention comprises coating a surface of a base material with acoating material composition comprising a material that has ahydrolyzable group having Si or Ti and a fluorocarbon group and a fineparticle or a whisker, and hydrolyzing a coating film comprising thecoating material composition in an atmosphere containing moisture toprovide a film comprising at least a fine particle or a whisker and amicrocrystalline polymer having a fluorocarbon group that is crosslinkedby a siloxane bond or a titanium-oxygen bond. This structure canefficiently provide a coating film that has excellent durability,super-water-repellency, and excellent water separation.

In the above method, it is preferable that the hydrolyzable group havingSi or Ti is at least one selected from the group consisting of ahalosilyl group, an alkoxysilyl group, a silane group, an isocyanatesilane group, an alkoxytitanium group, a titanium halide group, and anisocyanate titanium group. This can provide a coating film that has aless impurity content, excellent durability, super-water-repellency, andexcellent water separation.

The present invention can comprise a film that comprises amicrocrystalline polymer having at least a fluorocarbon group and has arough surface. It is convenient in durability if the microcrystallinepolymer having a fluorocarbon group is at least crosslinked by asiloxane bond or a titanium-oxygen (--TiO--) bond. Also, it is furtherexcellent in durability if the microcrystalline polymer having afluorocarbon group that is crosslinked by a siloxane bond or atitanium-oxygen bond is manufactured by a hydrolysis reaction. Also,when the roughness of the surface is at least 0.1 to 100 μm, preferably0.5 to 50 μm, very high water repellency can be obtained, and thereforea coating film that has excellent water separation can be obtained.Particularly, when the roughness is 0.5 to 50 μm, a contact angle of160° to water can be obtained.

As a method for manufacturing such a coating film, a method comprising,after coating a surface of a base material with a material that has ahydrolyzable group having at least Si or Ti and a fluorocarbon group,hydrolyzing a coating film comprising the material in an atmospherecontaining moisture to grow a microcrystal can be used. As a result, afilm comprising a microcrystalline polymer having a fluorocarbon groupthat is at least crosslinked by a siloxane bond or a titanium-oxygenbond can be manufactured. When the hydrolyzable group having Si or Ti isa halosilyl group, an alkoxysilyl group, a silane group, an isocyanatesilane group, an alkoxytitanium group, a titanium halide group, or anisocyanate titanium group, a hydrolysis reaction can occur very easily,which is convenient in the manufacturing process.

When applying the present invention to a heat exchanger fin, themanufacturing method comprises a step of roughening a surface of a basematerial, a step of coating the surface of the base material with amaterial that has a hydrolyzable group having Si or Ti and afluorocarbon group, and a step of hydrolyzing a coating film comprisingthe material in an atmosphere containing moisture to provide a filmcomprising a microcrystalline polymer having a fluorocarbon group thatis crosslinked by a siloxane bond or a titanium-oxygen bond. Accordingto the above method, a heat exchanger fin that has excellent durability,super-eater-repellency, and excellent water separation can beefficiently manufactured.

In the above method, it is preferable that the hydrolyzable group havingSi or Ti is at least one organic group selected from the groupconsisting of a halosilyl group, an alkoxysilyl group, a silane group,an isocyanate silane group, an alkoxytitanium group, a titanium halidegroup, and an isocyanate titanium group. This structure can provide aheat exchanger fin that has a lower impurity content, excellentdurability, super-water-repellency, and excellent water separation. Acoating apparatus for a hydrolysis-hardening coating material cancomprise a dipping vessel for putting a hydrolysis-hardening coatingmaterial in, and a seal gas supplying means provided in a gas phase partof the dipping vessel for preventing a surface of thehydrolysis-hardening coating material from being in direct contact withmoisture in the air. Thus, in coating with a hydrolysis-hardeningcoating material, the coating process can be continuously performed byusing an open system, while preventing the degradation of the coatingmaterial due to the moisture in air.

In the above apparatus. it is preferable that the seal gas is dry air ora gas heavier than air. When using dry air, it is preferable tocontinuously circulate the dry air. When using a gas heavier than air,the gas is occasionally circulated according to the degree of diffusion.

A coating method for a hydrolysis-hardening coating material comprisesthe use of a coating apparatus comprising a dipping vessel for ahydrolysis-hardening coating material comprising a compound that has ahydrolyzable group having at least Si or Ti and a fluorocarbon group anda nonaqueous solvent, and a seal gas supplying means connected to a gasphase part of the dipping vessel. In particular, the method comprisessupplying a seal gas for sealing so that a surface of ahydrolysis-hardening coating material put in the dipping vessel is notin direct contact with moisture in the air, and coating a surface of abase material with the hydrolysis-hardening coating material by passingthe seal gas through, dipping the base material in thehydrolysis-hardening coating material, and pulling the base material up.According to this method, coating can be performed, while preventing thedegradation of a hydrolysis-hardening coating material due to themoisture in the air. Of course, the coating process can be continuouslyperformed by using an open system.

In the above method, it is preferable that the hydrolyzable group havingSi or Ti is at least one organic group selected from the groupconsisting of a halosilyl group, an alkoxysilyl group, a silane group,an isocyanate silane group, an alkoxytitanium group, a titanium halidegroup, and an isocyanate titanium group. The above compound hasexcellent hydrolysis-hardenability and can be hardened in a very shorttime in hardening after coating with the coating material.

In the above method, it is preferable to manufacture a film thatcomprises a microcrystalline polymer having a fluorocarbon group that isat least crosslinked by a siloxane bond or a titanium-oxygen bond, byhydrolyzing a hydrolysis-hardening coating material in an atmospherecontaining moisture to provide a hydrolysis-hardening coating materialhaving a microcrystalline state, after coating a surface of a basematerial with the hydrolysis-hardening coating material. According tothis method, in coating with a hydrolysis-hardening coating material, awater repellent coating film can be manufactured, while preventing thedegradation of the coating material due to the moisture in air.

In the above method, it is preferable that the base material is a fin ofa heat exchanger for an air conditioner. When applying it to a heatexchanger fin for an air conditioner, an energy-saving air conditionerhaving a very high efficiency and excellent amenity can be provided.

In the above method, it is preferable that the seal gas is dry air or agas heavier than air.

In the above method, it is preferable that the gas heavier than air isat least one gas selected from the group consisting of carbon dioxideand argon. The use of carbon dioxide or argon can efficiently preventthe moisture in air from diffusing into the coating material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show a manufacturing process of Example 1 of the presentinvention; FIG. 1A is a cross-sectional view of a base material; FIG. 1Bis a conceptual cross-sectional view in which a film that comprises amicrocrystalline polymer having a fluorocarbon group and has a roughsurface is formed on a surface of the base material, however, thepresent invention should not be limited to this conceptual view; FIG. 1Cis a conceptual cross-sectional view in which an X part of a surface ofthe base material in FIG. 1B is enlarged, however, the present inventionshould not be limited to this conceptual view;

FIG. 2 is a cross-sectional view for conceptually illustrating a coatingapparatus and a coating method of Example 4 of the present invention;

FIGS. 3A and 3B illustrate a surface treatment process in Example 2 ofthe present invention; FIG. 3C is a cross-sectional view in which a Ypart of a surface of the base material in FIG. 3B is enlarged;

FIGS. 4A and 4B are cross-sectional views for illustrating a surfacetreatment process in Example 3 of the present invention; and FIG. 4C isa cross-sectional view in which a Z part of a surface of the basematerial in FIG. 4B is enlarged.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention will be described belowreferring to FIG. 1.

FIGS. 1A-1C show a process for manufacturing a first water repellentcoating film of the present invention. FIG. 1A is a cross-sectional viewof a base material. FIG. 1B is a conceptual cross-sectional view inwhich a film that comprises a microcrystalline polymer having afluorocarbon group and has a rough surface is formed on a surface of thebase material. FIG. 1C is a conceptual cross-sectional view in which anX part of a surface of the base material in FIG. 1B is enlarged to amicron level. A fin 11 is for performing heat exchange action between anair conditioner and the outside air and is formed of an aluminium sheet,etc. that has excellent heat conductivity. A film 12 that comprises amicrocrystalline polymer having a fluorocarbon group and has a roughsurface prevents frosting and is formed of a microcrystalline polymerhaving a fluorocarbon group that is crosslinked by a siloxane bond.

In the above description, film 12 that comprises a microcrystallinepolymer having a fluorocarbon group and has a rough surface is formed ofa microcrystalline polymer having a fluorocarbon group that iscrosslinked by a siloxane bond. However, it is similarly practicablewith crosslinking by a titanium-oxygen (--TiO--) bond.

A second water repellent coating film of the present invention is formedof a film that comprises at least a fine particle or a whisker as a coreand a microcrystalline polymer having a fluorocarbon group that isformed to wrap the fine particle or the whisker, and has a roughsurface. It is convenient in durability if the microcrystalline polymerhaving a fluorocarbon group is at least crosslinked by a siloxane bondor a titanium-oxygen bond. Also, the durability is improved, if themicrocrystalline polymer having a fluorocarbon group that is crosslinkedby a siloxane bond or titanium-oxygen bond is manufactured by way of ahydrolysis reaction. Also, fine particles such as alumina, silica,glass, or fluororesin, or whiskers such as silica, alumina, bariumtitanate can be easily treated. By selecting the one in which theaverage diameter of a primary particle is 5 nm to 100 μm, preferably 7nm to 50 μm, and the roughness of a film surface after forming a coatingfilm is 0.1 to 100 μm, preferably 0.5 to 50 μm, very high waterrepellency can be obtained, and therefore a coating film that hasexcellent water separation can be obtained. In particular, when theroughness is 0.5 to 50 μm, a contact angle of 160° or more to water canbe obtained.

A method for manufacturing such a coating film comprises coating asurface of a base material with a coating material comprising a materialthat has a hydrolyzable group having at least Si or Ti and afluorocarbon group and a fine particle or a whisker, and hydrolyzing acoating film comprising the material and the fine particle or thewhisker in an atmosphere containing moisture to provide a coating filmhaving a microcrystalline state. As a result, a film comprising at leasta fine particle or a whisker and a microcrystalline polymer having afluorocarbon group that is crosslinked by a siloxane bond or atitanium-oxygen bond can be manufactured. When the hydrolyzable grouphaving Si or Ti is a halosilyl group, an alkoxysilyl group, a silanegroup, an isocyanate silane group, an alkoxytitanium group, a titaniumhalide group, or an isocyanate titanium group, a hydrolysis reaction canoccur very easily.

Suitable materials having a fluorocarbon group and a hydrolyzable groupinclude compounds having the following Formula 1 or 2.

Formula 1

    CF.sub.3 --(CF.sub.2).sub.n --(R).sub.m --SiX.sub.p Cl.sub.3-p

in which n represents 0 or an integer, R represents an alkylene group, avinylene group, an ethynylene group, an arylene group such as phenylenegroup, silicon, or a substituent having an oxygen atom, m represents 0or 1, X represents H, an alkyl group, an alkoxyl group, an isocyanategroup, a fluorine-containing alkyl group, or a fluorine-containingalkoxy group, p represents 0, 1, 2 or 3.

Formula 2

    CF.sub.3 --(CF.sub.2).sub.n --(R).sub.m --TiX.sub.p Cl.sub.2-p

in which n represents 0 or an integer, R represents an alkylene group, avinylene group, an ethynylene group, an arylene group such as phenylenegroup, silicon, or a substituent having an oxygen atom, m represents 0or 1, X represents H, an alkyl group, an alkoxyl group, an isocyanategroup, a fluorine-containing alkyl group, or a fluorine-containingalkoxy group, p represents 0, 1 or 2.

Specific examples of suitable materials in addition to the abovereagents include compounds such as the following:

(1) CF₃ CH₂ O(CH₂)₁₅ SiHCl₂

(2) CF₃ (CH₂)₂ Si(CH₃)₂ (CH₂)₁₅ SiCl₃

(3) CF₃ (CH₂)₆ Si(CH₃)₂ (CH₂)₉ Si(OCH₃)Cl₂

(4) CF₃ (CF₂)₇ (CH₂)₂ Si(CH₃)₂ (CH₂)₁₀ SiCl₃

(5) CF₃ COO(CH₂)₁₅ Si(NCO)Cl₂

(6) CF₃ (CF₂)₇ (CH₂)₂ SiCl₃

(7) CF₃ (CF₂)₇ (CH₂)₂ Si(NCO)₃

(8) CF₃ (CF₂)₅ (CH₂)₂ SiCl₃

(9) CF₃ (CF₂)₅ (CH₂)₂ Si(NCO)₃

(10) CF₃ (CF₂)₅ (CH₂)₂ SiCH₃ Cl₂

(11) CF₃ (CF₂)₇ C₆ H₄ SiCl₃

(12) CF₃ (CF₂)₇ (CH₂)₂ TiCl₂

(13) CF₃ (CF₂)₅ (CH₂)₂ Ti(OCH₃)Cl

(14) CF₃ (CF₂)₇ C₆ H₄ TiCl₂

While only linear chain molecules are illustrated here, the molecule maybe a molecule having a side chain group if it is a material that has ahydrolyzable group having at least Si or Ti and a fluorocarbon group.

Also, a method for roughening a surface of a base material may be usedtogether. In this case, any art-recognized technique such as polishingby a metal brush, sand blasting, or a chemical etching method can beused. However, the method need not be limited to these methods as longas it can roughen a surface of a base material at a micron level. Inthis case, when the roughness of a surface of a base material is atleast 0.1 to 50 μm, preferably 0.3 to 10 μm, very high water repellencycan be obtained, and therefore a coating film that has excellent waterseparation can be obtained. Particularly, when the roughness is 0.3 to10 μm, a contact angle of 170° or more to water can be obtained.

Also, any method such as a dipping method, a spraying method, or a brushcoating method can be applied as a coating method for a material thathas a hydrolyzable group having at least Si or Ti and a fluorocarbongroup. Furthermore, the material may be directly used for coating, or itmay be diluted with a nonaqueous solvent such as normal paraffin orxylene for coating. When diluting the material, by using a nonaqueoussolvent that does not contain water at all, the volatility can be high,the time for coating and drying can be shortened, and also it isconvenient for protecting a hydrolyzable group before coating.

Also, the amount of the material that has a hydrolyzable group having atleast Si or Ti and a fluorocarbon group is preferably 1 to 50% byweight. If the amount is less than this, the film becomes too thin,worsening the water repellency. If the amount is more than this, theviscosity of the solution can become too high, causing difficulty incoating.

Also, by adding at least one filler selected from the group consistingof a fine particle and a whisker in coating with a solution thatcontains the above material, the second coating film of the presentinvention, that is, a film that comprises a fine particle or a whisker,can be formed. In this case, the amount of the filler is preferably 1 to30% by weight. If the amount is less than this, the filler does notprovide the desired effect. If the amount is greater than this, thecoating film can become fragile, decreasing its durability.

In the above solution, it is preferable that except for the materialthat has a hydrolyzable group having at least Si or Ti and afluorocarbon group and the filler, a nonaqueous organic solvent isemployed. Therefore, the amount of the nonaqueous organic solvent ispreferably in the range of 20 to 98% by weight.

Also, by forming such a thin film that comprises a microcrystallinepolymer having at least a fluorocarbon group and has a rough surface ona surface of the fin of the heat exchanger of an air conditioner, an airconditioner that does not require an extra heater for thawing, has veryhigh efficiency, and provides excellent amenity can be provided.

Next, a coating apparatus for a hydrolysis-hardening coating material ofthe present invention will be described by referring to FIG. 2.

FIG. 2 illustrates an example of a coating apparatus of the presentinvention, and it is a conceptual view of a coating apparatus that has adipping vessel 22 for putting a hydrolysis-hardening coating material 21in and a layer (gas seal layer) of a gas heavier than air (for example,carbon dioxide) 23 for preventing the contact of the coating materialand air that is provided on a surface of the hydrolysis-hardeningcoating material put in the dipping vessel 22. In FIG. 2, an assembledheat exchanger fin for an air conditioner 25 is dipped and pulled upacross the layer of a gas heavier than air 23 by using a lift 26, and istaken out in air, while continuously spraying a gas heavier than airfrom a nozzle for a gas heavier than air 24 on the surface of thecoating material in the dipping vessel in which the hydrolysis-hardeningcoating material is put, and producing the layer of a gas heavier thanair 23 for preventing the contact of the coating material and air on thesurface of the coating material. Thus, the coating apparatus allows forthe surface of the fin to be coated with the hydrolysis-hardeningcoating material, while the contact of hydrolysis-hardening coatingmaterial 21 and air is prevented, without the use of a cover. Because ofthis, continuous coating can be performed.

Next, the present invention will be described in more detail usingexamples.

In the following examples, a contact angle to water is measured by aWilhelmy method using Wetability measuring apparatus, MODEL WET-6000,RHESCA CO., LTD. In other words, a base material on which amicrocrystalline polymer is formed is inserted perpendicularly into thesurface of water, and a contact angle is measured by a stress from thesurface of water then. A contact angle in forward movement is calculatedby a stress when the base material is inserted, and a contact angle inbackward movement is calculated by a stress when the base material ispulled up. Also, a contact angle refers to an angle when a water dropstays still. A dynamic contact angle refers to a contact angle when awater drop slides down. The contact angle of the forward portion of awater drop is a contact angle in forward movement, and the contact angleof the backward portion of a water drop is a contact angle in backwardmovement.

EXAMPLE 1

A fin 11 that is made of well washed aluminium (Al) was previouslyprepared (FIG. 1A). Next, by using CF₃ (CF₂)₇ --(CH₂)₂ --SiCl₃ as amaterial that has a hydrolyzable group having at least Si or Ti and afluorocarbon group, and diluting it with cyclohexamethyl trisiloxane asa nonaqueous solvent at a concentration of 10 vol. %, a solution forforming a coating film was prepared. The fin was coated with thissolution to a thickness of 1 to 10 μm by a brush. Then, thecyclohexamethyl trisiloxane was vaporized in an atmosphere having arelative humidity of 75% (good results were obtained at 60% or more.) atroom temperature, and CF₃ (CF₂)₇ --(CH₂)₂ --SiCl₃ that remained on thefin was rapidly hydrolyzed with the moisture in the atmosphere. Then,the moisture in air and a --SiCl₃ group dehydrochlorinated to form thefollowing Formula 4. The reaction ended in about ten minutes, and amicrocrystalline polymer 12 that has a fluorocarbon group and iscrosslinked by a siloxane bond was formed on fin 11 (FIG. 1B). ##STR1##

This film was also covalently bonded to a surface of the base materialby a --SiO-- bond as shown in FIG. 1C (an enlarged view of an X part inFIG. 1B) and had little peeling and very high weather resistance. Also,the roughness of the surface was in the range of 1 to 40 μm, and thecontact angle to water was 171°. Furthermore, a dynamic contact anglewas measured assuming the application to an air conditioner. The resultsare shown in Table 1.

When using a material that has a Ti hydrolyzable group, similar resultswere obtained. Furthermore, when the hydrolyzable group having Si or Tiwas a halosilyl group, an alkoxysilyl group, a silane group, anisocyanate silane group, an alkoxytitanium group, a titanium halidegroup, or an isocyanate titanium group, similar results were obtained.

When using a compound shown in the Formula 3 as a material that has afluorocarbon group and a hydrolyzable group, similar results wereobtained.

In the process of the above experiment, it has become clear that theapparent reaction speed of dehydrochlorination (a hydrolysis reaction inthe example), that is, the humidity in the reaction atmosphere, iscritical. By more detail examination, it has become clear that there isa close relationship between the roughness of the surface of the basematerial, the speed of the hydrolysis reaction, and the growth of themicrocrystal, and that the roughness of the surface of the coating filmcan be made greater as the reaction speed becomes higher. In theexperiment similar to Example 1, it has become clear that by setting thehumidity 35% or more, a difference in the COS θ of a contact anglebetween in the forward and backward movements of a water drop can be 0.1or less, which is practically preferable.

EXAMPLE 2

A fin 31 that is made of well washed Al was previously prepared (FIG.3A). Next, 5% by weight of silica fine particles having an averageparticle diameter of 20 nm (alumina or glass fine particles orfluororesin fine particles or oxide whiskers may be used) and CF₃ (CF₂)₇--(CH₂)₂ --SiCl₃ (a concentration of 10% by weight) as a coatingmaterial component compound that has a hydrolyzable group having Si orTi and a fluorocarbon group were diluted with a nonaqueous solvent ofnormal paraffin (a boiling point of 150° C.) for preparation. The fin 31that is made of Al was coated with this coating material for forming acoating film to a thickness of 1 to 10 μm by using a brush. Then, thenormal paraffin was vaporized in an atmosphere having a relativehumidity of 75% (good results were obtained at a relative humidity of60% or more) at room temperature, and the coating material componentcompound was rapidly hydrolyzed with the moisture in the atmosphere,with a fine particle 32 that remained on the fin being as a core. Then,the moisture in air and a --SiCl₃ group dehydrochlorinated, and acoating film shown by the Formula 4 has formed.

This reaction ended in about ten minutes, and a film 34 that comprises amicrocrystalline polymer 33 having a fluorocarbon group and beingcrosslinked by a siloxane bond and has a rough surface was formed on fin31 (FIG. 3B). This film was also bonded to a surface of the basematerial by a --SiO-- bond as shown in FIG. 3C and had little peelingand very high weather resistance. Also, the roughness of the surface was1 to 40 μm in average, and the contact angle to water was 172°.Furthermore, a dynamic contact angle was measured assuming theapplication to an air conditioner. The results are shown in Table 1.

When using a material that has a Ti hydrolyzable group, similar resultswere obtained. Furthermore, when the hydrolyzable group having Si or Tiwas a halosilyl group, an alkoxysilyl group, a silane group, anisocyanate silane group, an alkoxytitanium group, a titanium halidegroup, or an isocyanate titanium group, similar results were obtained.

EXAMPLE 3

A fin base material 41 that is made of well washed Al was previouslyprepared by rubbing an aluminium (Al) sheet by a wire brush, and forminga roughness of 8 to 10 μm on the surface (FIG. 4A). Next, CF₃ (CF₂)₇--(CH₂)₂ --SiCl₃ as a material that has a hydrolyzable group having atleast Si or Ti and a fluorocarbon group was diluted with toluene as anonaqueous solvent at a concentration of 10% by weight for preparation.The fin base material was coated with this solution for forming acoating film to a thickness of 1 to 10 μm by a brush. Then, the toluenewas vaporized in an atmosphere having a relative humidity of 40% (goodresults were obtained at a relative humidity of 30 to 60%.) at roomtemperature, and CF₃ (CF₂)₇ --(CH₂)₂ --SiCl₃ that remained on the finbase material was rapidly hydrolyzed with the moisture in theatmosphere. Then, the moisture in air and a --SiCl₃ groupdehydrochlorinated, and a coating film shown by the Formula 4 wasformed.

The reaction almost ended in about ten minutes, and a film 42 thatcomprises a microcrystalline polymer having a fluorocarbon group andbeing crosslinked by a siloxane bond and has a rough surface was formedon fin base material 41 (FIG. 4B). This film 42 had little peeling dueto the effect of being also bonded to the surface of the base materialby a --SiO-- bond and the effect of the roughness of the surface of thebase material as is shown in FIG. 4C as an enlarged view of a Z part,and had very high weather resistance. Also, the roughness of the surfacewas 1 to 12 μm, and the contact angle to water was 174°. Furthermore, adynamic contact angle was measured assuming the application to an airconditioner. The results are shown in Table 1.

Also, the suitable roughness of the surface of the base material is inthe range of 0.1 to 50 μm. Similar results were obtained by using anymethod for roughening a surface, such as a sand blasting method or anetching method, as long as this surface roughness can be realized.

The humidity of the atmosphere in which toluene is vaporized aftercoating with the solution for forming a coating film by a brush dependson the surface roughness. For example, when the surface roughness is inthe range of 0.1 to 8 μm, the relative humidity is preferably 60% (goodresults were obtained at a relative humidity of 40 to 80%.). When thesurface roughness is in the range of 8 to 50 μm, the relative humidityis preferably 40% (good results were obtained at a relative humidity of30 to 60%.). When the humidity was lower than this, a microcrystallinepolymer was not formed, and the water repellency was decreased. Also,when the humidity was higher than the above range, the film becamefragile, and the durability was decreased.

Also, when using a material that has a Ti hydrolyzable group, similarresults were obtained. Furthermore, when the hydrolyzable group havingSi or Ti was a halosilyl group, an alkoxysilyl group, a silane group, anisocyanate silane group, an alkoxytitanium group, a titanium halidegroup, or an isocyanate titanium group, similar results were obtained.The results are shown in Table 1.

EXAMPLE 4

Previously, using an coating apparatus that has a dipping vessel 22 forputting a hydrolysis-hardening coating material 21 in and a nozzle 24for blowing off a carbon dioxide gas as a gas heavier than air (argongas has the same effect) as shown in FIG. 2, a predetermined amount of ahydrolysis-hardening coating material (a coating material that isprepared by diluting CF₃ (CF₂)₇ --(CH₂)₂ --SiCl₃ with normal paraffin (aboiling point of 150° C.) at a concentration of 10% by weight) is put inthe dipping vessel 22. Immediately after that, a constant amount ofcarbon dioxide gas is continuously blown off from nozzle 24 for a carbondioxide gas. Thus, a carbon dioxide gas layer (gas seal layer) 23 forpreventing the contact of the coating material and air is formed on asurface of the coating material.

Then, a heat exchanger fin for an air conditioner 25 that is completelyassembled is dipped and pulled up across carbon dioxide gas layer 23 byusing a lift 26, and is taken out in air. Coating operation wascontinuously performed for a day. As a result, the coating material wasnot degraded at all, without becoming cloudy with a color of white. Inother words, the fin surface could be uniformly coated with thehydrolysis-hardening coating material to a thickness of 1 to 10 μm,while continuously preventing the contact of hydrolysis-hardeningcoating material 21 and the moisture in the air, without closing a coverof the dipping vessel. Also, no degradation of the hydrolysis-hardeningcoating material due to the moisture in the air occurred.

Then, the normal paraffin was vaporized in an air atmosphere having arelative humidity of 75% (although good results were obtained at arelative humidity of 60% or more.) at room temperature, and CF₃ (CF₂)₇--(CH₂)₂ --SiCl₃ that remained on the fin was rapidly hydrolyzed withthe moisture in the atmosphere. Then, the moisture in air and a --SiCl₃group dehydrochlorinated, and a coating film shown by the Formula 4 wasformed.

The reaction ended in about ten minutes, and a film that comprises amicrocrystalline polymer having a fluorocarbon group and beingcrosslinked by a siloxane bond and has a rough surface was formed on aheat exchanger fin 25. This film was also bonded to a surface of thebase material by a --SiO-- bond and had little peeling and very highweather resistance. Also, the roughness of the surface was 1 to 40 μm,and the contact angle to water was 171°. Furthermore, a dynamic contactangle was measured assuming the application to an air conditioner. Theresults are shown in Table 1.

When using a material that has a Ti hydrolyzable group, similar resultswere obtained. Furthermore, when the hydrolyzable group having Si or Tiwas a halosilyl group, an alkoxysilyl group, a silane group, anisocyanate silane group, an alkoxytitanium group, a titanium halidegroup, or an isocyanate titanium group, similar results were obtained.

COMPARATIVE EXAMPLE 1

Dehydrochlorination was performed, on the same condition as in Example 1except for the reaction atmosphere, at room temperature in air having arelative humidity of 20%. In this case, similarly, the reaction ended inabout 14 to 15 minutes, and a film that comprises a microcrystallinepolymer having a fluorocarbon group and being crosslinked by a siloxanebond and has a rough surface was formed on a heat-dissipating sheet.This film was also bonded to a surface of the base material by a --SiO--bond and had little peeling and very high weather resistance. However,the roughness of the surface was 0.1 μm or less with large waviness, andthe contact angle to water was 149°. The measurement result of thedynamic contact angle is shown in Table 1 with Example 1.

COMPARATIVE EXAMPLE 2

On the same condition as in Example 4 except for eliminating the carbondioxide gas layer, that is, the case where a seal gas is not blown off,the surface of the coating material became cloudy with a color of whitein about one hour, and the coating material was degraded.

                  TABLE 1                                                         ______________________________________                                                      *            difference                                                       **        ***    in COS θ *1                              ______________________________________                                        Example 1     175       162    0.042                                            Example 2 175 169 0.0055                                                      Example 3 177 172 0.0083                                                      Example 4 175 163 0.040                                                       Comparative Example 153 84 0.99                                             ______________________________________                                         *a contact angle to water (°)                                          **a contact angle in forward movement                                         ***a contact angle in backward movement                                       *1A difference in cos θ is a difference between respective         

cosines of a contact angle in forward movement (θa) and a contact anglein backward movement (θr), that is, cos θ r-cos θa. This difference incosine is related to the fall angle of a water drop (an angle when awater drop starts sliding) α as follows:

    m g sin α=2Rγ(cos θr-cos θa)

in which m represents the mass of a water drop, g represents theacceleration of gravity, R represents the radius of the surface of awater drop in contact with a surface of a base material, and γrepresents the surface tension of water. In other words, as a differencein cosine is smaller, a water drop falls more easily.

As is apparent from Table 1, the ones that were treated in the examplesof the method of the present invention peeled little by rubbing with afinger, and had a very high dynamic contact angle. Also, a difference inCOS θ could be 0.01 or less, and the surface properties with littleadhesion of a water drop could be achieved.

Furthermore, by comparing Examples 1 and 3, it has become clear that adifference in COS θ can be 0.01 or less, and higher performance thanthat of a flat base material is obtained by setting the roughness of thesurface of the base material be in the range of 0.1 to 50 micron. Also,as is apparent from Table 1, the ones that were treated by the method ofthe present invention had a very high dynamic contact angle. Also, adifference in the COS θ of a contact angle between in forward andbackward movements could be 0.05 or less, and the surface propertieswith little adhesion of a water drop could be achieved.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limitative, the scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A water repellent coating film comprising apolymer comprising a fluorocarbon group formed on a surface of asubstrate, wherein the polymer of the film is a microcrystalline polymerand has a rough surface, and at least some of the molecules forming thefilm are covalently bonded to the surface of the substrate.
 2. The waterrepellent coating film according to claim 1, wherein themicrocrystalline polymer comprises a fluorocarbon group and iscrosslinked by at least one bond selected from the group consisting of asiloxane (--SiO--) bond and a titanium-oxygen (--TiO--) bond.
 3. Thewater repellent coating film according to claim 1, wherein the filmfurther comprises a core comprising at least one material selected fromthe group consisting of a fine particle and a whisker.
 4. The waterrepellent coating film according to claim 3, wherein themicrocrystalline polymer having a fluorocarbon group is crosslinked byat least one bond selected from the group consisting of a siloxane(--SiO--) bond and a titanium-oxygen (--TiO--) bond and is chemicallybonded to the core.
 5. The water repellent coating film according toclaim 2, wherein the microcrystalline polymer having a fluorocarbongroup that is crosslinked by at least one bond selected from the groupconsisting of a siloxane bond and a titanium-oxygen (--TiO--) bond isformed by a hydrolysis reaction.
 6. The water repellent coating filmaccording to claim 1, wherein the roughness of the surface is in therange of 0.1 to 100 μm.
 7. The water repellent coating film according toclaim 1, wherein the roughness of the film is in the range of 0.1 to 100μm.
 8. The water repellent coating film according to claim 1, whereinthe film is cloudy with a color of white or is opaque.
 9. The waterrepellent coating film according to claim 1, wherein the water repellentcoating film is formed on a surface of a fin of a heat exchanger. 10.The water repellent coating film according to claim 9, wherein a surfaceof a base material of the fin is roughened.
 11. The water repellentcoating film according to claim 10, wherein the roughness of the surfaceof the base material is in the range of 0.1 to 50 μm.
 12. The waterrepellent coating film according to claim 9, wherein the fin isincorporated in a heat exchange part of an air conditioner.